1. Field of the Invention
The present invention relates to a zoom lens system having at least three lens groups and, and more precisely, relates to a zoom lens system in which the zoom adjustment can be mechanically and precisely carried out. The present invention also relates to an adjusting method using the zoom lens system.
2. Description of the Related Art
In a zoom lens system, a zoom adjustment to make a focal plane thereof coincident with a film surface (image forming surface of a camera) without moving the focal plane during zooming must be carried out. Strictly speaking, an adjustment to prevent the focal plane of the zoom lens from moving during zooming is referred to as a zoom adjustment, and an adjustment to make the focal plane coincident with the film surface (image forming surface) is referred to as a back adjustment, respectively. In the specification of the present application, the zoom adjustment includes both the above-mentioned zoom adjustment and the back adjustment. Conventionally, the zoom adjustment is carried out by mechanically adjusting the positions of the constituent lens groups of the zoom lens system upon assembly and adjustment of the zoom lens system.
In recent electrically controlled zoom lens systems in which the positions of the lens groups can be pulse-controll ed, the amount of zoom adjustment is stored in a ROM for each discrete focal length and each discrete object distance as pulse-number data. When a shutter release button is depressed upon photographing, the positions of the lens groups are adjusted in accordance with focal length data and object distance data (pulse-number data), taking into account the amount of zoom adjustment. In this type of zoom lens system, no mechanical adjustment is necessary.
However, in a zoom lens system which is marketed as a separate lens unit, such as an interchangeable lens, a mechanical adjustment must be carried out. In conventional zoom lens systems, the shift (deviation) of the focal plane at the short focal length extremity and the long focal length extremity is corrected by a mechanical adjustment at two points in the variable focal length. However, it is impossible to precisely correct the shift of focal plane at an intermediate focal length. In a zoom lens system whose depth of focus is small, focal plane shift at an intermediate focal length is not negligible.
It is an object of the present invention to provide a zoom lens system having at least three lens groups, in which zoom adjustment can be mechanically and precisely carried out.
To achieve the object mentioned above, according to an aspect of the present invention, a zoom lens system is provided, which includes at least three lens groups, in which the distance between at least two lens groups of the at least three lens groups is varied during zooming, the zoom lens system including a first adjustment mechanism for mechanically adjusting a first lens group of the at least three lens groups in the optical axis direction upon assembly and adjustment; a second adjustment mechanism for mechanically adjusting a second lens group of the at least three lens groups, which is different from the first lens group, in the optical axis direction upon assembly and adjustment; and a third adjustment mechanism for mechanically adjusting a third lens group of the at least three lens groups, which is different from the first and second lens group, in the optical axis direction upon assembly and adjustment.
According to another aspect of the present invention, a zoom lens system is provided, which includes at least three lens groups, in which the distance between at least two lens groups of the at least three lens groups is varied during zooming, the zoom lens system including a first adjustment mechanism for mechanically adjusting a first lens group, of the at least three lens groups, closest to the object side in the optical axis direction upon assembly and adjustment; a second adjustment mechanism for mechanically adjusting a second lens group, of the at least three lens groups, closest to the image side in the optical axis direction upon assembly and adjustment; and a third adjustment mechanism for mechanically adjusting a variable power lens group, of the at least three lens groups, upon assembly and adjustment; wherein the variable power lens group is one of moved and not moved during zooming in the optical axis direction.
According to another aspect of the present invention, an adjusting method for a zoom lens system is provided, which includes at least three lens groups in which the distance between at least two lens groups of the at least three lens groups is varied during zooming, the zoom lens system being provided with a first adjustment mechanism which adjusts a position of a first lens group of the at least three lens groups closest to the object side in the optical axis direction, upon assembly and adjustment; a second adjustment mechanism which adjusts a position of one of all of the at least three lens groups and a lens group closest to the image side in the optical axis direction, upon assembly and adjustment; and a third adjustment mechanism which adjusts a position of a variable power lens group of the at least three lens groups in the optical axis direction upon assembly and adjustment, wherein the variable power lens group is one of moved and not moved during zooming. The adjusting method includes performing a correction to make the positions of the focal planes at the short focal length extremity and at the long focal length extremity of the zoom lens system coincident with an image forming plane of a camera, using the first and second adjustment mechanisms; measuring a focal plane shift at an intermediate focal length of the zoom lens system and performing an adjustment to make the positions of the focal planes, of the zoom lens system, at the short focal length extremity, at the long focal length extremity and at the intermediate focal length coincident with each other; and performing a correction to make the positions of the focal plane, of the zoom lens system, at the short focal length extremity and at the long focal length extremity coincident with the image forming surface of the camera, using the first and second adjustment mechanisms.
Preferably, the following condition (1) is satisfied:
0.01 less than |xcex94P(fM)/xcex94t3| less than 0.9xe2x80x83xe2x80x83(1)
wherein
xcex94t3 designates the amount of adjustment performed by the third adjustment mechanism, and xcex94P(fM) designates the focal plane shift at the intermediate focal length after the positions of the focal planes at the short focal length extremity and at the long focal length extremity are made coincident with the image forming surface of the camera.
According to another aspect of the present invention, an adjusting method for a zoom lens system is provided, which includes at least three lens groups in which the distance between at least two lens groups of the at least three lens groups is varied during zooming, the zoom lens system being provided with a first adjustment mechanism which adjusts a position of a first lens group of the at least three lens groups closest to the object side in the optical axis direction, upon assembly and adjustment; a second adjustment mechanism which adjusts a position of one of all of the at least three lens groups and a lens group closest to the image side in the optical axis direction, upon assembly and adjustment; and a third adjustment mechanism which adjusts a position of a variable power lens group of the at least three lens groups which is one of moved and not moved during zooming in the optical axis direction, upon assembly and adjustment. The adjusting method includes measuring the focal plane shifts xcex94P(fS), xcex94P(fM) and xcex94P(fL) at the short focal length extremity fS, at an intermediate focal length fM, and at the long focal length extremity fL, respectively, from a reference point; calculating the amounts of adjustment xcex94t1, xcex94t2 and xcex94t3 by the first, second and third adjustment mechanisms, using the measurements of xcex94P(fs), xcex94P(fM) and xcex94P(fL); by the following sensitivity matrix A of the first, second and third adjustment mechanisms which is represented by the following formula 4; and by the following formula 5:                     A        =                  [                                                                                          ∂                                          Pc                      ⁡                                              (                                                  f                          S                                                )                                                                                                  ∂                                          t                      1                                                                                                                                        ∂                                          Pc                      ⁡                                              (                                                  f                          S                                                )                                                                                                  ∂                                          t                      2                                                                                                                                        ∂                                          Pc                      ⁡                                              (                                                  f                          S                                                )                                                                                                  ∂                                          t                      3                                                                                                                                                                ∂                                          Pc                      ⁡                                              (                                                  f                          M                                                )                                                                                                  ∂                                          t                      1                                                                                                                                        ∂                                          Pc                      ⁡                                              (                                                  f                          M                                                )                                                                                                  ∂                                          t                      2                                                                                                                                        ∂                                          Pc                      ⁡                                              (                                                  f                          M                                                )                                                                                                  ∂                                          t                      3                                                                                                                                                                ∂                                          Pc                      ⁡                                              (                                                  f                          L                                                )                                                                                                  ∂                                          t                      1                                                                                                                                        ∂                                          Pc                      ⁡                                              (                                                  f                          L                                                )                                                                                                  ∂                                          t                      2                                                                                                                                        ∂                                          Pc                      ⁡                                              (                                                  f                          L                                                )                                                                                                  ∂                                          t                      3                                                                                                    ]                                    Formula        ⁢                  xe2x80x83                ⁢        4                                                      [                                                                                                                                                        Δ                          ⁢                                                      xe2x80x83                                                    ⁢                          t1                                                                                                                                                              Δ                          ⁢                                                      xe2x80x83                                                    ⁢                          t2                                                                                                                                                                                      Δ                    ⁢                                          xe2x80x83                                        ⁢                    t3                                                                        ]                    =                      -                                          A                                  -                  1                                            ⁡                              [                                                                                                                                                                                        P                              ⁡                                                              (                                                                  f                                  S                                                                )                                                                                                                                                                                                                        P                              ⁡                                                              (                                                                  f                                  M                                                                )                                                                                                                                                                                                                                                            P                        ⁡                                                  (                                                      f                            L                                                    )                                                                                                                    ]                                                    ⁢                  
                ⁢                  (                      Wherein            ,                                          "LeftBracketingBar"                A                "RightBracketingBar"                            ≠              0                                )                                    Formula        ⁢                  xe2x80x83                ⁢        5            
and moving the at least three lens groups by the respective amounts of adjustment xcex94t1, xcex94t2 and xcex94t3 by the first, second and third adjustment mechanisms.
The present disclosure relates to subject matter contained in Japanese Patent Application No. 11-162573 (filed on Jun. 9, 1999) which is expressly incorporated herein by reference in its entirety.